1. Field of the Invention
This invention relates to an apparatus for cooling integrated circuit chips and, in particular, to a thermal conduction module and a method of adjustment and assembly thereof.
2. Description of Related Art
Integrated circuit chips mounted in an array on substrates present special cooling difficulties. While chip size has increased over the years and power usage is more efficient than in the past, work is still needed on cooling systems and methods to remove the relatively high density power dissipated by the chips. The prior art is replete with different types of thermal conduction modules (TCMs) designed to enclose and cool integrated circuit chips mounted on ceramic-glass substrates. In some instances, the TCMs utilize liquid coolants to cool the chips, such as those described in U.S. Pat. Nos. 5,239,200, 5,294,830 and 5,177,667, issued to the assignee of this application. Another approach to cooling has been described in U.S. Pat. No. 4,500,945, also assigned to the assignee of this application, by the use of pistons contacting the chips within the TCMs to remove heat.
A further approach in cooling chips in TCMs has been to utilize a thermally conductive medium, such as high thermal conductivity pastes, between the top of the integrated circuit chip mounted on the substrate and the lower surface of the cover plate facing the substrate. An example of the useful, stable, high solid content, high thermal conductivity paste is disclosed in U.S. Pat. No. 5,098,609. This compound can be applied as a thin film between the top of the chip and the lower surface of the cover of the TCM. In order to properly control the amount of heat removed from the integrated circuit chip, it is desirable to determine a gap of a specified and desired fixed distance between the top of the chip and the lower surface of the cover, and to fill that space completely with the thermally conductive medium such as the aforementioned paste.
Prior art methods of setting the proper gap between the top surface of the chip and the lower surface of the cover have utilized an integral spacer within the thermal conduction module to control size of the gap. This spacer is normally integral with the cover plate and extends around the periphery of the area of the substrate on which the integrated surface chips are mounted.
Glass ceramics which are normally used as substrate materials for the integrated circuit chips are brittle and easy to break, and must be handled with care. The substrates are normally mounted in a base plate of the TCM which encompasses the edges of the substrate. The cover plate is normally secured to this base plate surrounding the substrate following assembly of the TCM. It has been found that the use of the integral spacer in the TCM can contribute to breakage of the glass ceramic substrates when the cover plate is fastened too tightly to the base plate. This has been found to occur because the integral spacer transfers force directly to the substrate when the fasteners, typically screws or bolts around the periphery of the cover plate, are tightened down to the base plate. The substrate, which is contained within the base plate by a lip extending within its periphery, is then subject to excessive and uneven forces from the spacer which may not be in direct line with the lip of the base plate. The application of excessive force to the fasteners will then tend to break the substrates near the lip of the base plates. Because parallelism of the lower surface of the cover plate and the tops of the integrated surface chips must be maintained in all assembled parts, an even distribution force must be applied around the periphery of the thermal conduction module.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a thermal conduction module which may be assembled with a controlled gap between the lower surface of the cover plate and the upper surface of the integrated circuit chip without causing excessive force and breakage to the chip substrate, whereby a desired thermally conductive medium may be applied between the chip and the cover plate to effect controlled heat removal and cooling of the chip.
It is another object of the present invention to provide a method of assembling a thermal conduction module which reduces the possibility of breakage of the chip substrate while maintaining a controlled gap between the cover plate and the top surface of the integrated circuit chips for insertion of a thermally conductive medium.
A further object of the invention is to provide a thermal conduction module in which the cover plate may be secured to the base plate with higher loading on the fasteners with a reduced possibility of damage to the chip substrate.
It is yet another object of the present invention to provide an apparatus for cooling integrated circuit chips mounted on a substrate by providing an adjustable spacer between the apparatus cover plate and base plate which does not bear directly on the substrate.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.